Journal
TRAFFIC
Volume 2, Issue 1, Pages 37-50Publisher
MUNKSGAARD INT PUBL LTD
DOI: 10.1034/j.1600-0854.2001.020106.x
Keywords
endocytosis; fluorescent; NBD; phospholipid; phosphotidylcholine; phosphotidylethanolamine; S. cerevisiae; secretion; vacuole; yeast
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Funding
- NIGMS NIH HHS [GM52410] Funding Source: Medline
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R21GM052410] Funding Source: NIH RePORTER
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The internalization and distribution of fluorescent analogs of phosphatidylcholine (M-C-6-NBD-PC) and phosphatidylethanolamine (M-C-6-NBD-PE) were studied in Saccharomyces cerevisiae. At normal growth temperatures, M-C-6-NBD-PC was internalized predominantly to the vacuole and degraded. M-C-6-NBD-PE was internalized to the nuclear envelope/ER and mitochondria, was not transported to the vacuole, and was not degraded. At 2 degreesC, both were internalized to the nuclear envelope/ER and mitochondria by an energy-dependent. N-ethyl-maleimide-sensitive process, and transport of M-C-6-NBD-PC to and degradation in the vacuole was blocked. Internalization of neither phospholipid was reduced in the endocytosis-defective mutant, end4-1.. However, following pre-incubation at 37 degreesC, internalization of both phospholipids was inhibited at 2 degreesC and 37 degreesC in sec mutants defective in vesicular traffic. The sec18/NSF mutation was unique among the sec mutations in further blocking M-C-6-NBD-PC translocation to the vacuole suggesting a dependence on membrane fusion. Based on these and previous observations, we propose that M-C-6-NBD-PC and M-C-6-NBD-PE are transported across the plasma membrane to the cytosolic leaflet by a protein-mediated, energy-dependent mechanism. From the cytosolic leaflet, both phospholipids are spontaneously distributed to the nuclear envelope/ER and mitochondria. Subsequently, M-C-6-NBD-PC, but not M-C-6-NBD-PE, is sorted by vesicular transport to the vacuole where it is degraded by lumenal hydrolases.
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